Control device of linear compressor drive system

ABSTRACT

A control apparatus for a linear compressor driving system is disclosed for stabilizing the behavior of a piston and thereby protecting the increase in noise vibration caused by collision and the reduction in reliability. This control apparatus stabilizes the behavior of the piston by including: an unstableness detecting means, which directly or indirectly detects that the behavior of the piston is unstable and then outputs an unstableness detection signal; and an unstableness avoiding means which is operated in accordance with the unstableness detection signal.

TECHNICAL FIELD

[0001] The present invention relates to a control apparatus for a linearcompressor driving system used for a refrigerator, an air conditionerand the like.

BACKGROUND ART

[0002] In recent years, the necessity of a higher efficiency of arefrigerating apparatus has been increased from the viewpoint of earthenvironment protection and energy saving. A compressor using a linearmotor has been widely used in order to make its efficiency higher andreduce its manufacturing cost, because of its simple mechanicalconfiguration. However, in order to run the linear compressor at a highefficiency, it is necessary to run a piston in a reciprocating mannerwhile keeping a clearance at a top dead center of the piston small. Atthe same time, the control of the refrigerating performance of thecompressor is carried out, correspondingly to the size of the clearanceat the top dead center. As mentioned above, this requires the controlsthat are not carried out in a reciprocating compressor of a conventionalconnecting rod type.

[0003] As a conventional controlling method of a linear compressor,there is a method described in Japanese Laid Open Patent ApplicationJP-A 2000-121180. FIG. 10 is a sectional view showing a linearcompressor that is a main unit in a linear compressor driving system asa control target to be controlled in accordance with the presentinvention, and FIG. 11 is a block diagram showing the configuration ofthe conventional control apparatus for controlling the linear compressordriving system.

[0004] In FIGS. 10 and 11, reference numeral 1 denotes a linearcompressor, 2 denotes a sealed casing, and 3 denotes a compressor body.Also, reference numeral 4 denotes a linear motor, 5 denotes a cylinder,6 denotes a piston, and 7 denotes a cylinder head. The motor 4 isprovided with: a stator 4 a having a coil 4 c; and a movable element 4 bhaving a permanent magnet. The movable element 4 b is fixed to thepiston 6. Also, reference numeral 10 denotes a compression room composedof the cylinder 5 and the piston 6. The compressor body 3 is composedof: a movable device 11 constituted by the movable element 4 b of themotor 4 and the piston 6 and the like; and a fixed device 12 constitutedby the cylinder 5 and the stator 4 a of the motor 4 and the like. Also,reference numeral 14 denotes an elastic device. It is attached to themovable device at its center 14 a and attached to the fixed device.

[0005] Also, reference numeral 16 denotes a power supply unit, 17denotes a voltage determining means, and 18 denotes an ambienttemperature detecting means. Reference numeral 19 denotes a heatexchanger constituted by an evaporator 19 a and a condenser 19 b. 20denotes an expansion valve. The linear compressor 1, the condenser 19 b,the expansion valve 20 and the evaporator 19 a are linked throughpiping, and they form a system 21 in which refrigerant is circulated.

[0006] The operation of the conventional control apparatus for thelinear compressor driving system will be described below. The ambienttemperature detecting means 18 measures an ambient temperature andoutputs a temperature signal based on the temperature. The voltagedetermining means 17 outputs a voltage target value based on thetemperature signal. The power supply unit 16 outputs an alternatingcurrent in a shape of a sine wave to the linear compressor 1 at avoltage corresponding to the voltage target value.

[0007] The alternating current outputted from the power supply unit 16is sent to the coil of the motor 4 in the linear compressor 1 so that amagnetic field is generated by the current flowing through the coil.Thus, the movable element 4 b together with the piston 6 is reciprocatedby the magnetic force acting between the movable element 4 b and thepermanent magnet. At this time, the greater the amplitude of the piston6, the higher the voltage of the power supply unit 16, and the greaterthe amplitude of the piston, the stronger the refrigerating performancein the system 21.

[0008] By the way, in the case of the refrigerator, the necessaryrefrigerating performance is different depending on the ambienttemperature. That is, if the ambient temperature is high, the thermalload on the refrigerator is high, which requires the strongrefrigerating performance. On the other hand, if the ambient temperatureis low, the necessary refrigerating performance becomes weak. However,at this time, if the refrigerating performance is excessively strong, acompression ratio is raised to thereby reduce the system efficiency.Hence, the proper refrigerating performance needs to be selected fromthe viewpoint of the system efficiency.

[0009] Thus, the voltage determining means 17 outputs a high voltagetarget value if the ambient temperature is high, and outputs a lowvoltage target value if the transistor is low. Consequently, the powersupply unit 16 outputs the voltage necessary for the properrefrigerating performance to the linear compressor 1.

[0010] Also, a frequency of an alternating power supply generated by thepower supply unit 16 is given as a resonant frequency mainly determinedby a mass of the movable device 11 and a spring constant of the elasticdevice 14 in the linear compressor 1 and the like. Consequently, thespring force of the elastic device 14 can be effectively used for thereciprocating motion of the movable device 11.

[0011] However, in the case of the above-mentioned conventionalconfiguration, when a tip of the piston 6 gets toward the cylinder head7, the influence of the action force on the piston and the like bringsabout the unstable behavior, such as the variation of the position atthe top dead center of the piston and the like. There may be a case thatthe movable member such as the piston and the like collides with thefixed member such as a valve plate and the like. This may be caused bythe following influences. That is, the action force on the pistonresults not only from the spring force through a resonant spring butalso from the gas compression force of the compression room. Moreover,this action force has a non-linear property. In addition, even a motorthrust is varied by a compression load.

[0012] The unstable behavior of the piston and the collision between themovable member and the fixed member bring about the problems of noiseand vibration, and the strong collision leads to the problem of the dropin the reliability of the valve placed in the cylinder head and thelike.

[0013] Even if they do not collide, the severe variation in the behaviorof the piston may cause the noise. Moreover, since the circulationamount of the refrigerant is varied, this has the problem that apredetermined performance can not be obtained.

DISCLOSURE OF THE INVENTION

[0014] In view of the above-mentioned problems, it is therefore anobject of the present invention to stabilize the behavior of a pistonand thereby protect the occurrence of noise vibration and furtherprotect the reduction in the reliability of a compressor and therebyimprove the reliability. Also, the object is to stabilize the behaviorof the piston and obtain the predetermined refrigerating performance andthereby improve the system efficiency.

[0015] Also, the fear of a collision occurrence is little under theoperating condition in which a top clearance is large. Thus, this hasthe following problem. That is, even if the control for stabilizing thebehavior is performed on the slight variation in the top dead center ofthe piston, there is no effect of the collision protection. Moreover,the electric power for the control is consumed.

[0016] Another object of the present invention is to reduce theoccurrence of the circuit loss caused by the execution of the controlwithout executing the control under the operating condition in which thenecessity of the control is little.

[0017] Also, in order to keep a top dead center position of the pistonconstant, when a feedback control is carried out by detecting a positionof the piston, a current and a voltage and by changing a supply voltagein accordance with the difference from a target value for each constantcycle, if a cycle of the control and a change amount of the supplyvoltage are unsuitable, on the contrary, there may be a case that thebehavior of the piston becomes unstable.

[0018] Another object of the present invention is to avoid the unstablephenomenon of the piston caused by the unsuitable feedback control andcarry out a stable operation.

[0019] The present invention is a control apparatus for a linearcompressor driving system, which is used for a linear compressor drivingsystem including: a linear compressor having a linear motor and apiston; and a power supply unit for supplying an electric power to thelinear motor, including: an unstableness detecting means for detectingthat a behavior of the piston is unstable and outputting an unstablenessdetection signal; and an unstableness avoiding means that is operated soas to act on the linear compressor driving system in accordance with theunstableness detection signal and thereby avoid the unstable state. Thishas the effect of protecting the reduction in the reliability and theincrease in the noise vibration, which are caused by the collisionbetween the movable member and the fixed member since the behavior ofthe piston becomes unstable.

[0020] Another embodiment of the present invention is a controlapparatus for a linear compressor driving system, which is used for alinear compressor driving system including: a linear compressor having alinear motor and a piston; and a power supply unit for supplying anelectric power to the linear motor, including: an operating conditiondetecting means for detecting at least one of a displacement of thepiston, an ambient temperature, a temperature at any part of the linearcompressor driving system, and an operating pressure, and thenoutputting a detection signal; an unstableness detecting means, which ifthe detection signal of the operating condition detecting meanssatisfies a predetermined condition, estimates that a behavior of thepiston is unstable, and then outputs an unstableness detection signal;and an unstableness avoiding means that is operated so as to act on thelinear compressor driving system in accordance with the unstablenessdetection signal and thereby avoid the unstable state. This has theeffect of: protecting the reduction in the reliability and the increasein the noise vibration, which are caused by the collision between themovable member and the fixed member since the behavior of the pistonbecomes unstable and; and reducing the loss of the control circuitnecessary for the control since the unstableness avoiding control iscarried out only when it is required.

[0021] Another embodiment of the present invention further includes adisplacement detecting means for detecting a displacement of the piston.The unstableness detecting means is designed so as to output theunstableness detection signal in accordance with an output of thedisplacement detecting means. Thus, this has the effect of directlydetecting that the behavior is unstable, from the displacement of thepiston,

[0022] Another embodiment of the present invention further includes asound and vibration detecting means for detecting sound or vibration ofthe compressor. The unstableness detecting means is designed so as tooutput the unstableness detection signal in accordance with an output ofthe sound and vibration detecting means. Thus, this has the effect ofindirectly detecting that the behavior of the piston is unstable, fromthe sound and the vibration.

[0023] Another embodiment of the present invention further includes avoltage current detecting means for detecting a voltage or a currentoutputted by the power supply unit. The unstableness detecting means isdesigned so as to output the unstableness detection signal in accordancewith an output of the voltage current detecting means. Thus, this hasthe effect of indirectly detecting that the behavior of the piston isunstable, from the voltage or the current of the power supply unit.

[0024] Another embodiment of the present invention further includes apressure detecting means for detecting a pressure of the system. Theunstableness detecting means is designed so as to output theunstableness detection signal in accordance with an output of thepressure detecting means. Thus, this has the effect of indirectlydetecting that the behavior of the piston is unstable, from the pressureof the system.

[0025] Another embodiment of the present invention further includes anambient temperature detecting means for detecting an ambienttemperature. The unstableness detecting means is designed so as tooutput the unstableness detection signal in accordance with an output ofthe ambient temperature detecting means. Thus, this has the effect ofindirectly detecting that the behavior of the piston is unstable, fromthe ambient temperature.

[0026] Another embodiment of the present invention further includes atemperature detecting means for detecting a temperature of the system.The unstableness detecting means is designed so as to output theunstableness detection signal in accordance with an output of thetemperature detecting means. Thus, this has the effect of indirectlydetecting that the behavior of the piston is unstable, from thetemperature of a refrigerating system.

[0027] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change a voltagewaveform or a current waveform outputted by the power supply unit inaccordance with the unstableness detection signal. Thus, this has theeffect of reducing the unstable phenomenon of the piston by changing thethrust property of a motor.

[0028] Another embodiment of the present invention further includes awaveform memory for storing waveforms having a plurality of patterns,and the unstableness avoiding means is designed so as to output, fromthe power supply, the voltage or the current based on the waveformstored in the waveform memory, in accordance with the unstablenessdetection signal. Thus, the motor thrust property effective for avoidingthe unstableness can be selected. Hence, this has the effect of reducingthe unstable phenomenon of the piston,

[0029] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change an impedance ofthe motor in accordance with the unstableness detection signal. Thus, amethod of changing the coil of the linear motor from a parallel wiringto a series wiring in accordance with the unstableness detection signaland the like are used to change the impedance of the motor. Thus, thewaveform of the current flowing through the motor is changed, and thethrust property of the motor is changed. Consequently, this has theeffect of relaxing the unstable behavior of the piston.

[0030] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change an air blowingamount to a heat exchanger in accordance with the unstableness detectionsignal. Thus, by changing the air blowing amount, the pressure of thesystem is varied to thereby changing the acting force on the piston.Hence, this has the effect of reducing the unstable behavior.

[0031] Another embodiment of the present invention is such that an airblowing amount changing means is designed so as to change a rotationalspeed and an air blowing path of an air blower. Thus, the change of themenables the pressure of the system to be changed, and thereby enablesthe action force on the piston to be changed. Hence, this has the effectof reducing the unstable behavior.

[0032] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change a frequencyoutputted by the power supply unit in accordance with the unstablenessdetection signal. Thus, this has the effect of reducing the unstablephenomenon of the piston due to the change of the operating frequency.

[0033] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change the voltage orthe current of the power supply unit in accordance with the unstablenessdetection signal. Thus, this has the effect of increasing the topclearance of the piston to thereby avoid the collision, or selecting thestroke that does not lead to the occurrence of the unstable phenomenon.

[0034] Another embodiment of the present invention includes: a detectingmeans for detecting a current, a voltage or a piston displacement; atarget value setting means for setting a target value of the current orthe voltage or the piston displacement in accordance with an operatingcondition; a timer means for outputting a start signal at apredetermined interval; and a changing means for comparing an output ofthe detecting means with the target value in accordance with the startsignal, and changing the voltage or the current outputted by the powersupply unit at a predetermined change amount, correspondingly to thedifference from the target value, wherein the unstableness avoidingmeans is designed so as to change at least one of the change amount ofthe detecting means and the output interval of the start signal of thetimer means, in accordance with the unstableness detection signal. Thus,this has the effect of avoiding the unstable phenomenon of the pistoncaused by the feedback control at the top dead center position of thepiston.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] These and other objects and features will become more readilyapparent from the following detailed description taken in conjunctionwith the accompanying drawings in which:

[0036]FIG. 1 is a block diagram showing a first embodiment of a controlapparatus for a linear compressor driving system according to thepresent invention;

[0037]FIG. 2 is a waveform view of a current which is detected by acurrent detecting means in the first embodiment of the present inventionand sent from a power supply unit to a linear compressor;

[0038]FIG. 3 is a flowchart showing an operation of an unstablenessdetecting means in the first embodiment of the present invention;

[0039]FIG. 4 is a flowchart showing an operation of an unstablenessavoiding means in the first embodiment of the present invention;

[0040]FIG. 5 is a block diagram showing a second embodiment of a controlapparatus for a linear compressor driving system according to thepresent invention;

[0041]FIG. 6 is a block diagram showing a third embodiment of a controlapparatus for a linear compressor driving system according to thepresent invention;

[0042]FIG. 7 is a block diagram showing a fourth embodiment of a controlapparatus for a linear compressor driving system according to thepresent invention;

[0043]FIG. 8 is a block diagram showing a fifth embodiment of a controlapparatus for a linear compressor driving system according to thepresent invention;

[0044]FIG. 9 is a block diagram showing a sixth embodiment of a controlapparatus for a linear compressor driving system according to thepresent invention;

[0045]FIG. 10 is a sectional view showing a conventional linearcompressor; and

[0046]FIG. 11 is a block diagram showing a conventional linearcompressor driving system and its control apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0047] Embodiments of a control apparatus for a linear compressordriving system according to the present invention will be describedbelow with reference to FIGS. 1 to 9. By the way, the same symbols aregiven to the same configurations as the conventional technique, andtheir detailed explanations are omitted.

First Embodiment

[0048]FIG. 1 is a block diagram showing a control apparatus for a linearcompressor driving system according to a first embodiment of the presentinvention.

[0049] In FIG. 1, reference numeral 30 denotes a current detecting meansfor measuring a current of a power supply sent to a linear compressor 1from a power supply unit 31. Reference numeral 32 denotes anunstableness detecting means for outputting an unstableness detectionsignal in accordance with an output of the current detecting means 30.

[0050] If the variation in a top dead center of a piston is great, theaction force on the piston, such as a compression power and the like, isvaried to thereby vary even a current flowing through a motor. Thus, theunstableness detecting means 32 extracts the variation in the peak valueof the current measured by the current detecting means. If the variationin the peak value in a certain period is greater than a predeterminedvalue, it estimates and judges that the behavior of the piston becomesunstable, and outputs the unstableness detection signal.

[0051] Here, the unstableness detecting means 32 is described in detailwith reference to FIGS. 2 and 3. FIG. 2 is a waveform view of thecurrent, which is detected by the current detecting means 30 in thefirst embodiment and sent to the linear compressor 1 from the powersupply unit 31. FIG. 3 is a flowchart showing the operation of theunstableness detecting means 32 in the first embodiment. In FIG. 2, tindicates a current detection cycle, and n detections are carried out inone detection cycle. Then, the manner when the detection values of npeak currents are obtained is shown, as illustrated by black points inthe waveform. The current detection values are represented by I(K-n+1),. . . I(K-2), . . . I(K-1) and I(K).

[0052]FIG. 3 is the flowchart showing the operation of CPU when theunstableness detecting means 32 is constituted by the CPU (CentralProcessing Unit) (not shown). At first, at a step S1, an initializationis carried out so as to reset the maximum current Imax and the minimumcurrent value Imin in previous measurement values to zero. Next, J=K-n+1is calculated at a step S2. Here, K is a predetermined constant, and nis a predetermined number of measurements per cycle, and J is a variableobtained as the calculation result. Next, whether or not the variable Jis greater than the constant K is judged at a step S3. Since J<K duringthe n measurements, the operating flow proceeds to a step S4, and acurrent value I(J) is detected. Next, if the current value I(J) detectedat a step S5 is greater than the Imax, the operating flow proceeds to astep S6, and the I(J) is defined as a new Imax. On the other hand, ifthe current value I(J) is not greater than the Imax at the step S5, theoperating flow proceeds to a step S7, and whether or not the currentvalue I(J) is less than the Imin is judged. If the current value I(J) isless than the Imin, the I(J) is defined as a new Imin at a step S8. Ifthe current value I(J) is not less than the Imin at the step S7, theoperating flow proceeds to a step S9. Even if the operations at thesteps S6 to S8 have been ended, the operating flow proceeds to the stepS9. At the step S9, the variable J is incremented by 1, and theoperating flow returns back to the step S3. The n repetitions of themeasurements at the steps S3 to S9 lead to J<K, and the operating flowproceeds to a step S10. At the step S10, the difference between the Imaxand the Imin is calculated to then judge whether or not this difference(Imax−Imin) is greater than a constant M. If the difference is greaterthan the constant M, the operating flow proceeds to a step S11. Then, itis judged to be an unstable state, and an unstable flag is set to YES.On the other hand, if the difference is less than the constant M, theoperating flow proceeds to a step S12, and it is judged not to be theunstable state, and the unstable flag is set to NO.

[0053] Reference numeral 33 denotes an unstableness avoiding means. Whenthe unstableness detection signal is inputted, it outputs a frequencychange signal to the power supply unit 31. When the frequency changesignal is inputted to the power supply unit 31, the power supply unit 31changes the frequency of the power supply sent to the compressor 1.Thus, changing the operating frequency of the linear compressor canavoid the condition that the piston behavior becomes unstable.

[0054] Here, the unstableness avoiding means 33 is described in detailwith reference to FIG. 4. FIG. 4 is a flowchart showing the operationwhen the unstableness avoiding means 33 in the first embodiment isconstituted by the CPU. By the way, when it is constituted by the sameCPU as the CPU constituting the unstableness detecting means 32, theprocesses in FIG. 4 can be configured by an interrupting processcorresponding to the process of FIG. 3 and the like. At a step S21 inFIG. 4, the unstable flag set at the steps S11, S12 in FIG. 3 ismonitored. Then, if the unstable flag is YES, the operating flowproceeds to a step S22, and the frequency of the driving current of thelinear compressor is lowered by ΔH₁. On the other hand, if the unstableflag is NO, the operating flow proceeds to a step S23. The frequency ofthe driving current of the linear compressor is kept in its originalstate.

[0055] By the way, as the consideration result in our company, even ifan operating pressure condition is changed in the actual apparatusoperation such as a refrigerator or the like to thereby bring about theunstable behavior of a piston, the fact that the unstable behavior isremoved by changing the frequency of the power supply by several Hz isexperimentally confirmed. Although the obvious reason with regard tothis causal relation is not still proved, it may be considered that themotor thrust, the pressure within the compression room, the behavior ofthe valve and the like contribute to the causal relation.

[0056] As mentioned above, the control apparatus for the linearcompressor driving system in this embodiment is provided with: thedetecting means for detecting the current of the power supply; theunstableness detecting means for indirectly detecting that the behaviorof the piston is unstable, in accordance with the output of thedetecting means, and outputting the unstableness detection signal; andthe unstableness avoiding means for changing the frequency of the powersupply in accordance with the unstableness detection signal. Even if thepiston behavior becomes unstable, this control apparatus stabilizes itby adjusting the frequency of the power supply. Thus, this can protectthe occurrence of the noise vibration caused by the collision and thereduction in the reliability.

Second Embodiment

[0057]FIG. 5 is a block diagram showing a control apparatus for a linearcompressor driving system according to a second embodiment of thepresent invention.

[0058] In FIG. 5, reference numeral 40 denotes a sound and vibrationdetecting means 40 constituted by a vibration pickup, and it is attachedto a compressor and detects sound and vibration. Also, reference numeral41 denotes an unstableness detecting means 41.

[0059] If the behavior of the piston becomes unstable and the movablemember of the compressor body 3 (refer to FIG. 10) collides with thefixed member, the collision causes the collisional sound and vibrationthat are greater than the typical case to be generated in thecompressor. When the collision is induced and the output of the soundand vibration detecting means is greater than a predetermined value, theunstableness detecting means 41 judges that the piston is unstable, andoutputs the unstableness detection signal.

[0060] Reference numeral 42 denotes an unstableness avoiding means. Ifthe unstableness detection signal is inputted, it outputs a voltage dropsignal to a voltage determining means 43. The voltage determining means43 usually outputs a voltage target value corresponding to an output ofthe ambient temperature detecting means 18 and controls an outputvoltage of the power supply unit 16. However, if the voltage drop signalis inputted, the voltage determining means 43 outputs a voltage targetvalue lower than the usual value, which results in the drop in the powersupply voltage of the linear compressor 1. Thus, the unstable conditionin which the amplitude of the piston is reduced to bring about thecollision is removed.

[0061] Also, if the output of the ambient temperature detecting means 18is less than the predetermined value, the sound and vibration detectingmeans 40, the unstableness detecting means 41 and the unstablenessavoiding means 42 stop their functions.

[0062] The collision between the movable member and the fixed member iseasier induced as a top clearance is smaller. When the top clearance islarge, the possibility of the collision becomes almost rare. Thus, ifthe ambient temperature is low and the operation can be carried out at asmall refrigerating performance, the top clearance is widely open.Hence, the possibility of the collision is said to be almost zero.

[0063] Thus, in the condition that the ambient temperature is low, thesound and vibration detecting means 40, the unstableness detecting means41 and the unstableness avoiding means 42 are not required. Hence, thestop of their functions enables the reduction in the electric powerconsumption.

[0064] As mentioned above, the control apparatus for the linearcompressor driving system in this embodiment is provided with: the soundand vibration detecting means for detecting the sound and the vibrationof the compressor; the unstableness detecting means for outputting theunstableness detection signal in accordance with the output of the soundand vibration detecting means; the unstableness avoiding means forchanging the voltage or the current of the power supply in accordancewith the unstableness detection signal; and the detecting means fordetecting the ambient temperature. Only if the output of the detectingmeans satisfies the predetermined condition, the unstableness detectingmeans and the unstableness avoiding means are actuated. Thus, if thepiston behavior becomes unstable to thereby bring about the collisionbetween the movable member and the fixed member in the compressor body,the collision is detected from the vibration, and the voltage sent tothe compressor is dropped. Hence, the collision is removed, and theoccurrence of the noise and the vibration and the reduction in thereliability are protected. Moreover, the unstableness detecting meansand the unstableness avoiding means are stopped in the operatingcondition that the unstable behavior of the piston is not induced. Henceit is possible to reduce the electric power consumption.

Third Embodiment

[0065]FIG. 6 is a block diagram showing a control apparatus for a linearcompressor driving system according to a third embodiment of the presentinvention.

[0066] In FIG. 6, reference numeral 50 denotes a displacement detectingmeans, which is attached to a compressor, for measuring the displacementof a piston.

[0067] Reference numeral 51 denotes an unstableness detecting means,which detects the variation in the top dead center of the piston fromthe output of the displacement detecting means 50, and outputs theunstableness detection signal if the variation in the top dead center isgreater than a predetermined value.

[0068] Reference numeral 52 denotes an unstableness avoiding means,which outputs a constant voltage waveform in a usual case. However, ifthe unstableness detection signal is inputted, the unstableness avoidingmeans 52 selects a voltage waveform different from that outputted untilthis time, from waveforms stored in a waveform memory 53, and outputsit.

[0069] A power supply unit 54 amplifies the voltage waveform outputtedfrom the unstableness avoiding means 52, to the voltage target valueoutputted from the voltage determining means 17, and then outputs to thecompressor 1.

[0070] Thus, when the behavior of the piston becomes unstable, thethrust property of the linear compressor can be changed to therebychange the action force on the piston and further stabilize the behaviorof the piston.

[0071] As mentioned above, the control apparatus for the linearcompressor driving system in this embodiment is provided with: thedisplacement detecting means for detecting the displacement of thepiston; the unstableness detecting means for outputting the unstablenessdetection signal in accordance with the output of the displacementdetecting means; the waveform memory for storing the waveforms of aplurality of patterns; and the unstableness avoiding means forsequentially outputting from the power supply the voltage waveformsstored in the waveform memory in accordance with the unstablenessdetection signal. Then, if the behavior of the piston becomes unstable,the waveform of the thrust of the linear motor is changed to therebystabilize the piston behavior.

Fourth Embodiment

[0072]FIG. 7 is a block diagram showing a control apparatus for a linearcompressor driving system according to a fourth embodiment of thepresent invention.

[0073] In FIG. 7, reference numeral 60 denotes an unstableness detectingmeans, which preliminarily stores an ambient temperature at which thebehavior of the piston becomes unstable, as a predetermined value, andthen outputs the unstableness detection signal at the predeterminedambient temperature to the output of an ambient temperature detectingmeans. Reference numeral 61 denotes an unstableness avoiding means,which changes an impedance of a motor by using a method of changing awiring of a linear motor of a compressor from a parallel wiring to aseries wiring, in accordance with the unstableness detection signal, andthe like. In association with this change, the waveform of the currentflowing through the motor is changed, and the thrust property of themotor is also changed. Thus, it is possible to stabilize the behavior ofthe motor.

[0074] As mentioned above, the control apparatus for the linearcompressor driving system in this embodiment is provided with: theambient temperature detecting means for detecting the ambienttemperature; the unstableness detecting means for outputting theunstableness detection signal in accordance with the output of theambient temperature detecting means; and the unstableness avoiding meansfor changing the impedance of the motor in accordance with theunstableness detection signal. When the behavior of the piston becomesunstable, the impedance of the motor can be changed to thereby changethe waveform of the thrust of the liner motor and further stabilize thepiston behavior.

Fifth Embodiment

[0075]FIG. 8 is a block diagram showing a control apparatus for a linearcompressor driving system according to a fifth embodiment of the presentinvention. In FIG. 8, reference numeral 70 denotes a condenser, 71denotes an expansion valve, and 72 denotes an evaporator. Including acompressor 1, they generate the refrigerating cycle of the refrigerator.By the way, the condenser 70 and the evaporator 72 are the heatexchangers, respectively, as well known. Also, the combination of themconstitutes the heat exchanger. Reference numeral 73 denotes an airblower placed near the evaporator. Cold air generated in the evaporator72 is sent into the refrigerator by the air blower 73.

[0076] Also, reference numeral 74 is a pressure detecting means attachedto the compressor 1. Reference numeral 74A denotes an unstablenessdetecting means, which judges that the behavior of the piston becomesunstable if an output of the pressure detecting means 74 satisfies apredetermined pressure condition, and outputs the unstableness detectionsignal.

[0077] Reference numeral 75 denotes an unstableness avoiding means,which when receiving the unstableness detection signal from theunstableness detecting means 74A, increases the air blowing amount ofthe air blower 73 to thereby raise a temperature of the evaporator 72and increase a low pressure. Consequently, the operating pressurecondition is changed, and the action force on the piston is changed tothereby stabilize the behavior of the piston.

[0078] As mentioned above, the control apparatus for the linearcompressor driving system in this embodiment is provided with: thepressure detecting means for detecting the pressure of the system; theunstableness detecting means for outputting the unstableness detectionsignal in accordance with the output of the pressure detecting means;and the unstableness avoiding means for changing the air blowing amountto the heat exchanger in accordance with the unstableness detectionsignal. When the behavior of the piston becomes unstable, the airblowing amount to the heat exchanger can be changed to thereby changethe pressure condition. Also, the action force on the piston can bechanged to thereby stabilize the piston behavior.

[0079] By the way, this embodiment is designed such that the pressuredetecting means is defined as the air blower jointly placed in the heatexchanger. However, the similar effect can be attained even by using adifferent means such as a valve that can change the pressure conditionin the refrigerating system.

Sixth Embodiment

[0080]FIG. 9 is a block diagram showing a control apparatus for a linearcompressor driving system according to a sixth embodiment of the presentinvention.

[0081] In FIG. 9, reference numeral 80 denotes a displacement detectingmeans, which detects a position of the piston and outputs a top deadcenter position signal of the piston. Reference numeral 81 denotes atarget value setting means, which outputs a standard value of a top deadcenter position of the piston. Reference numeral 82 denotes a timermeans, which outputs a start signal for each constant period. Also,reference numeral 83 denotes a changing means, which when receiving thestart signal from the timer means 82, changes a voltage setting value ata predetermined change amount for the difference between the standardvalue outputted by the target value setting means 81 and the top deadcenter position signal outputted by the displacement detecting means 80,and outputs the voltage setting value.

[0082] Also, reference numeral 84 denotes an unstableness detectingmeans, which stores the top dead center position signal outputted by thedisplacement detecting means 80, and if a value of a variation in aconstant temporal width exceeds a predetermined value, judges it to beunstable, and then outputs the unstableness detection signal. Referencenumeral 85 denotes an unstableness avoiding means, which when theunstableness detecting means outputs the unstableness detection signal,outputs a cyclic time setting signal to the timer means 82, and changesthe cycle of the start signal output of the timer means 82.

[0083] As a result, it is possible to protect the increase in thevariation of the top dead center position caused by the unsuitabletiming of the control in the feedback control for the top dead centerposition. Thus, the stable control can be carried out.

[0084] As mentioned above, the control apparatus for the linearcompressor driving system in this embodiment is provided with: thetarget value setting means for setting the predetermined target value onthe basis of the operating condition; the detecting means for detectingthe displacement of the piston; the unstableness detecting means fordetecting that the piston is at the unstable behavior and outputting theunstableness detection signal; the unstableness avoiding means forsuppressing or avoiding the unstableness in accordance with theunstableness detection signal; the timer means for outputting the startsignal at the predetermined interval; and the changing means forcomparing the output of the detecting means with the target value inaccordance with the start signal and changing the voltage or the currentof the power supply at the predetermined change amount, on the basis ofthe difference from the target value. Then, the unstableness avoidingmeans can avoid the unstableness of the piston behavior caused by thefeedback control, since the changing means changes the output timing ofthe start signal of the timer means, for the difference between theoutput of the detecting means and the target value, and thereby relaxesthe unstableness.

INDUSTRIAL APPLICABILITY

[0085] As mentioned above, the present invention include: theunstableness detecting means for directly or indirectly detecting thatthe behavior of the piston is unstable and outputting the unstablenessdetection signal; and the unstableness avoiding means to be operated inaccordance with the unstableness detection signal. Thus, this canprotect the unstable behavior of the piston and protect the reduction inthe reliability and the occurrence of the noise vibration, which arecaused by the collision.

[0086] Another embodiment of the present invention further includes thedetecting means for detecting at least one of the displacement of thepiston, the ambient temperature, the system temperature, and thepressure condition. The unstableness detecting means and theunstableness avoiding means are designed so as to act only if the outputof the detecting means satisfies the predetermined condition. Hence, theelectric power consumption can be reduced by designing that theoperations for detecting and avoiding the unstableness are not carriedout under the condition in which the collision is not induced.

[0087] Another embodiment of the present invention further includes thedisplacement detecting means for detecting the displacement of thepiston. The unstableness detecting means is designed so as to output theunstableness detection signal in accordance with the output of thedisplacement detecting means. Thus, this can directly detect theunstable behavior, from the displacement of the piston.

[0088] Another embodiment of the present invention further includes thesound and vibration detecting means for detecting the sound and thevibration of the compressor. The unstableness detecting means isdesigned so as to output the unstableness detection signal in accordancewith the output of the sound and vibration detecting means. Thus, thiscan indirectly detect the unstable phenomenon of the piston, from thesound and the vibration.

[0089] Another embodiment of the present invention further includes thedetecting means for detecting the voltage or the current of the powersupply. The unstableness detecting means is designed so as to output theunstableness detection signal in accordance with the output of thedetecting means. Thus, this can indirectly detect the unstablephenomenon of the piston, from the voltage or the current.

[0090] Another embodiment of the present invention further includes thepressure detecting means for detecting the pressure of the system. Theunstableness detecting means is designed so as to output theunstableness detection signal in accordance with the output of thepressure detecting means. Thus, this can indirectly detect the unstablephenomenon of the piston, from the current or the voltage.

[0091] Another embodiment of the present invention further includes theambient temperature detecting means for detecting the ambienttemperature. The unstableness detecting means is designed so as tooutput the unstableness detection signal in accordance with the outputof the ambient temperature detecting means. Thus, this can indirectlydetect the unstable phenomenon of the piston, from the ambienttemperature.

[0092] Another embodiment of the present invention further includes thetemperature detecting means for detecting the temperature of the system.The unstableness detecting means is designed so as to output theunstableness detection signal in accordance with the output of thetemperature detecting means. Thus, this can indirectly detect theunstable phenomenon of the piston, from the temperature of therefrigerating system.

[0093] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change the voltagewaveform or the current waveform of the power supply in accordance withthe unstableness detection signal. Thus, the thrust property of thelinear motor is changed. It is possible to stabilize the behavior of thepiston.

[0094] Another embodiment of the present invention further includes thewaveform memory for storing the waveforms having the plurality ofpatterns. The unstableness avoiding means is designed so as tosequentially output, from the power supply, the voltage or currentwaveform stored in the waveform memory, in accordance with theunstableness detection signal. Thus, the thrust property of the linearmotor is changed. It is possible to stabilize the behavior of thepiston.

[0095] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change the impedance ofthe motor in accordance with the unstableness detection signal. Thus,the thrust property of the linear motor is changed. It is possible tostabilize the behavior of the piston.

[0096] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change amount of theair blowing into the heat exchanger in accordance with the unstablenessdetection signal. Thus, the acting force by the pressure varies, and itis possible to stabilize the behavior of the piston.

[0097] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to open and close thevalve or change the air blowing amount to the heat exchanger inaccordance with the unstableness detection signal. Thus, the actingforce by the pressure is changed. It is possible to stabilize thebehavior of the piston.

[0098] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change the frequency ofthe power supply in accordance with the unstableness detection signal.Thus, it is possible to stabilize the behavior of the piston.

[0099] Another embodiment of the present invention is such that theunstableness avoiding means is designed so as to change the voltage orthe current of the power supply in accordance with the unstablenessdetection signal. Thus, this can increase the top clearance, protect thereduction in the reliability caused by the collision and protect theoccurrence of the noise and the vibration.

[0100] Another embodiment of the present invention is provided with: thedetecting means for detecting the current, the voltage or the pistondisplacement; the target value setting means for setting the targetvalue of the current or the voltage or the piston displacement inaccordance with the operating condition; the timer means for outputtingthe start signal at the predetermined interval; and the changing meansfor comparing the output of the detecting means with the target value inaccordance with the start signal, and changing the voltage or thecurrent of the power supply at the predetermined change amount,correspondingly to the difference from the target value, wherein theunstableness avoiding means is designed so as to change at least one ofthe change amount of the detecting means and the output interval of thestart signal of the timer means, in accordance with the unstablenessdetection signal. Thus, this can avoid the unstableness caused by thefeedback control of the piston position.

1. A control apparatus for a linear compressor driving system, which isused for a linear compressor driving system including: a linearcompressor having a linear motor and a piston; and a power supply unitfor supplying an electric power to said linear motor, comprising: anunstableness detecting means for detecting that a behavior of saidpiston is unstable and outputting an unstableness detection signal; andan unstableness avoiding means that is operated so as to act on saidlinear compressor driving system in accordance with said unstablenessdetection signal and thereby avoid the unstable state.
 2. A controlapparatus for a linear compressor driving system, which is used for alinear compressor driving system including: a linear compressor having alinear motor and a piston; and a power supply unit for supplying anelectric power to said linear motor, comprising: an operating conditiondetecting means for detecting at least one of a displacement of saidpiston, an ambient temperature, a temperature at any part of said linearcompressor driving system, and an operating pressure, and thenoutputting a detection signal; an unstableness detecting means, which ifthe detection signal of said operating condition detecting meanssatisfies a predetermined condition, estimates that a behavior of saidpiston is unstable, and then outputs an unstableness detection signal;and an unstableness avoiding means that is operated so as to act on saidlinear compressor driving system in accordance with said unstablenessdetection signal and thereby avoid the unstable state.
 3. The controlapparatus according to claim 1 or 2, wherein said unstableness detectingmeans has a displacement detecting means for detecting a displacement ofsaid piston.
 4. The control apparatus according to claim 1 or 2, whereinsaid unstableness detecting means has a sound and vibration detectingmeans for detecting sound or vibration of said compressor.
 5. Thecontrol apparatus according to claim 1 or 2, wherein said unstablenessdetecting means has a voltage current detecting means for detecting avoltage or a current outputted by said power supply unit.
 6. The controlapparatus according to claim 1 or 2, wherein said unstableness detectingmeans has a pressure detecting means for detecting a pressure of apredetermined portion of said linear compressor driving system.
 7. Thecontrol apparatus according to claim 1 or 2, wherein said unstablenessdetecting means has an ambient temperature detecting means for detectingan ambient temperature of said linear compressor driving system.
 8. Thecontrol apparatus according to claim 1 or 2, wherein said unstablenessdetecting means has a temperature detecting means for detecting atemperature of any part of said linear compressor driving system.
 9. Thecontrol apparatus according to claim 1 or 2, wherein said unstablenessavoiding means is designed so as to change a voltage waveform or acurrent waveform outputted by said power supply unit in accordance withsaid unstableness detection signal.
 10. The control apparatus accordingto claim 9, wherein said unstableness avoiding means is designed so asto output, from said power supply unit, voltage waveforms or currentwaveforms stored in a waveform memory, which stores voltage waveforms orcurrent waveforms having a plurality of patterns, in accordance withsaid unstableness detection signal.
 11. The control apparatus accordingto claim 1 or 2, wherein said unstableness avoiding means is designed soas to change an impedance of said linear motor in accordance with saidunstableness detection signal.
 12. The control apparatus according toclaim 1 or 2, wherein said unstableness avoiding means has an airblowing amount changing means for changing an air blowing amount to aheat exchanger connected to a linear compressor in accordance with saidunstableness detection signal.
 13. The control apparatus according toclaim 12, wherein said air blowing amount changing means is designed soas to change a rotational speed and/or change an air blowing path of anair blower for blowing an air to said heat exchanger.
 14. The controlapparatus according to claim 1 or 2, wherein said unstableness avoidingmeans is designed so as to change a frequency outputted by said powersupply unit in accordance with said unstableness detection signal. 15.The control apparatus according to claim 1 or 2, wherein saidunstableness avoiding means is designed so as to change a voltage valueor a current value outputted by said power supply unit in accordancewith said unstableness detection signal.
 16. The control apparatus for alinear compressor driving system according to claim 1 or 2, wherein saidunstableness detecting means includes: a detecting means for detectingat least one of a current of said power supply unit, a voltage of saidpower supply unit, and said piston displacement; a target value settingmeans for setting a target value of said current or said voltage or saidpiston displacement in accordance with an operating condition of saidlinear compressor; a timer means for outputting a start signal at apredetermined interval; and a changing means for comparing an output ofsaid detecting means with said target value in accordance with saidstart signal, and on the basis of a difference between them, changingsaid voltage or said current at a predetermined change amount, andwherein said unstableness avoiding means is designed so as to change atleast one of the change amount of said detecting means and the outputinterval of the start signal of said timer means, in accordance withsaid unstableness detection signal.